1. Field of the Invention
The present invention relates to a retaining seal material and an exhaust gas purifying apparatus.
2. Discussion of the Background
Particulate matter (hereinafter also referred to as PM) is contained in an exhaust gas exhausted from internal combustion engines, such as a diesel engine. In recent years, there has been a problem in that this PM causes harm to the environment and the human body. Additionally, since harmful gas components, such as CO, HC, or NOx, are also contained in the exhaust gas, there has also been a concern about the influence that the harmful gas components have on the environment and the human body.
Thus, as exhaust gas purifying apparatuses that trap the PM in the exhaust gas or purifies the harmful gas components, various exhaust gas purifying apparatuses that are constituted by an exhaust gas treatment body made of porous ceramics, such as silicon carbide or cordierite, a metal casing that houses the exhaust gas treatment body, and a retaining seal material that is disposed between the exhaust gas treatment body and the metal casing are suggested. This retaining seal material is disposed primarily for the purposes of preventing the exhaust gas treatment body from coming into contact with the metal casing covering an outer periphery thereof and being damaged due to vibration or impact generated by the traveling or the like of an automobile, and of preventing the exhaust gas from leaking from between the exhaust gas treatment body and the metal casing.
Here, since the internal combustion engines operate in a condition close to a theoretical air fuel ratio for the purpose of improvement in fuel consumption, the exhaust gas tends to have high temperature and high pressure. If the high-temperature and high-pressure exhaust gas reaches an exhaust gas purifying apparatus, the retaining seal material requires the retaining force of the exhaust gas treatment body that does not change even by slight fluctuation in the interval between the exhaust gas treatment body and the metal casing because the interval therebetween may fluctuate due to a difference in the coefficient of thermal expansion between the exhaust gas treatment body and the metal casing.
In order to improve the retaining performance of the retaining seal material, making inorganic particles adhere to the surfaces of the inorganic fibers is described in Japanese Unexamined Patent Application Publication No. 2002-206421 and PCT Japanese Translation Publication No. 2008-505276. Additionally, imparting inorganic particles to the surface of the retaining seal material is described in PCT Japanese Translation Publication No. 2009-508044 and PCT Japanese Translation Publication No. 2008-506886.
In the technique described in Japanese Unexamined Patent Application Publication No. 2002-206421, the inorganic particles are made to adhere to the surfaces of the inorganic fibers so that degradation of the surface pressure of the retaining seal material with time is not easily caused. Additionally, in the technique described in PCT Japanese Translation Publication No. 2008-505276, the inorganic particles are made to adhere to the surfaces of the inorganic fibers in order to improve the surface pressure of the retaining seal material.
In the technique described in PCT Japanese Translation Publication No. 2009-508044 and PCT Japanese Translation Publication No. 2008-506886, the inorganic particles are imparted to the surface of the retaining seal material in order to improve the frictional coefficient of the surface of the retaining seal material.